Atoms natural radioactive decay

He is found in natural gas deposits principally because alpha particles are produced during natural radioactive decay processes. These alpha particles are 4 He nuclei they obtain two electrons from the surrounding material to become helium atoms. This gaseous helium then accumulates with the natural gas trapped beneath the earth. Although other noble gases are produced by radioactive decay—notably 40 Ar—they are not produced in the large quantities that helium is. 

For very many years, the alchemist s dream of changing base metals into gold was ridiculed even by the most reputable of scientists. Although it was known that the nuclei of certain atoms undergo alteration in the course of natural radioactive decay, researchers inability to exercise any control over the nature or rate of these spontaneous decompositions probably did much to foster the belief that the nucleus of the atom was inviolate. However, in the year 1919 the English physicist Ernest Rutherford accomplished the first transmutation of an element, and this notable discovery was quickly followed by other equally significant developments. 

Radioactive nuclei emit a particles, 13 particles, positrons, or y rays. The equation for a nuclear reaction includes the particles emitted, and both the mass numbers and the atomic numbers must balance. Uranium-238 is the parent of a natural radioactive decay series. A number of radioactive isotopes, such as and C, can be used to date objects. Artificially radioactive elements are created by the bombardment of other elements by accelerated neutrons, protons, or a particles. Nuclear fission is the splitting of a large nucleus into smaller nuclei plus neutrons. When these neutrons are captured efficiently by other nuclei, an uncontrollable chain reaction can occur. Nuclear reactors use the heat... 

Lead, atomic number 82, is a member of Group 14 (IVA) of the Periodic Table. Ordinary lead is bluish grey and is a mixture of isotopes of mass number 204 (15%), 206 (23.6%), 207 (22.6%), and 208 (52.3%). The average atomic weight of lead from different origins may vary as much as 0.04 units. The stable isotopes are products of decay of three naturally radioactive elements (see Radioactivity, natural) comes from the uranium series (see Uraniumand... 

There are four modes of radioactive decay that are common and that are exhibited by the decay of naturally occurring radionucHdes. These four are a-decay, j3 -decay, electron capture and j3 -decay, and isomeric or y-decay. In the first three of these, the atom is changed from one chemical element to another in the fourth, the atom is unchanged. In addition, there are three modes of decay that occur almost exclusively in synthetic radionucHdes. These are spontaneous fission, delayed-proton emission, and delayed-neutron emission. Lasdy, there are two exotic, and very long-Hved, decay modes. These are cluster emission and double P-decay. In all of these processes, the energy, spin and parity, nucleon number, and lepton number are conserved. Methods of measuring the associated radiations are discussed in Reference 2 specific methods for y-rays are discussed in Reference 1. 

Rhenium, atomic wt 186.2, occurs in nature as two nucHdes Re [14391-28-7] mass 184.9530, in 37.500% abundance and Re [14391-29-8], mass 186.9560, in 62.500% abundance. The latter isotope is radioactive, emitting very low energy radiation and having a half-life estimated at 4.3 ( 0.5) X 10 ° yr. The radioactive decay of this isotope has been used to date accurately the time of Earth s formation. 

The nature of the radioactive decay is characteristic of the element it can be used to fingerprint die substance. Decay continues until bodi die original element and its daughter isotopes are non-radioactive. The half-life, i.e. die time taken for half of an element s atoms to become non-radioactive, varies from millions of years for some elements to fractions of a second for odiers. 

Uranium (symbol U atomic number 92) is the heaviest element to occur naturally on Earth. The most commonly occurring natural isotope of uranium, U-238, accounts for approximately 99.3 percent of the world s uranium. The isotope U-235, the second most abundant naturally occurring isotope, accounts for another 0.7 percent. A third isotope, U-234, also occurs uatiirally, but accounts for less than 0.01 percent of the total naturally occurring uranium. The isotope U-234 is actually a product of radioactive decay of U-238. 

Uranium-235 and U-238 behave differently in the presence of a controlled nuclear reaction. Uranium-235 is naturally fissile. A fissile element is one that splits when bombarded by a neutron during a controlled process of nuclear fission (like that which occurs in a nuclear reactor). Uranium-235 is the only naturally fissile isotope of uranium. Uranium-238 is fertile. A fertile element is one that is not itself fissile, but one that can produce a fissile element. When a U-238 atom is struck by a neutron, it likely will absorb the neutron to form U-239. Through spontaneous radioactive decay, the U-239 will turn into plutonium (Pu-239). This new isotope of plutonium is fissile, and if struck by a neutron, will likely split. 

Plutonium (symbol Pu atomic number 93) is not a naturally occurring element. Plutonium is formed in a nuclear reaction from a fertile U-238 atom. Since U-238 is not fissile, it has a tendency to absorb a neutron in a reactor, rather than split apart into smaller fragments. By absorbing the extra neutron, U-238 becomes U-239. Uranium-239 is not very stable, and undergoes spontaneous radioactive decay to produce Pu-239. 

The most abundant isotope is which constitutes almost 99% of the carbon in nature. About 1% of the carbon atoms are There are, however, small but significant differences in the relative abundance of the carbon isotopes in different carbon reservoirs. The differences in isotopic composition have proven to be an important tool when estimating exchange rates between the reservoirs. Isotopic variations are caused by fractionation processes (discussed below) and, for C, radioactive decay. Formation of takes place only in the upper atmosphere where neutrons generated by cosmic radiation react with nitrogen ... 

The stability of atoms - their property of being steadfast and remaining unchanged - is determined by the nature of their nuclei (see Textbox 12). Nuclei in which the number of neutrons is smaller than or equal to the number of protons are stable, while those in which the number of neutrons is larger than the number of protons are unstable. Unstable nuclei have a tendency to adjust the disparity between the number of neutrons and protons and become stable they may do so by one of two processes, by radioactive decay or nuclear fission. 

It has been hoped [20,21] that a method could be developed which would directly detect the radioatoms that are present in nature by an efficient ultra-sensitive mass spectrometer technique which would not itself depend upon the fact that the atoms being investigated are radioactive. The advantage of an efficient mass spectrometer system for long-lived radioisotopes can be seen from the equation for calculating the number of atoms present in a sample from its measured radioactive decay rate ... 

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